 Half as long as it's not high elevation. I prefer hot field work over cold field work. That's right sir. Sorry. Did Zach put out a recycling today? Is there recycling out? No. The most impractical rock hammer ever. Hi. Thank you all for coming again for our September meeting. Several announcements, I'm going to start it a little bit early. Before I get started, do we have any guests visiting us today? Hi Chris. You all want to introduce yourselves? Great, welcome. Are you a member? You should be one. Welcome Greg. Great. You guys going to Indy? Indianapolis for the GSA meeting? Oh great. Oh great. Chris got an NSF grant to work with students and community college students and go to different places including these great meetings. Great, thanks Chris. So any new members? We have Elliot here. Great. We're happy to have you. Thanks. You're replacing Craig who just retired, right? Craig Morgan, one of our past presidents. Earth Science Week is coming up and they are actively seeking volunteers. If you are unaware of Earth Science Week, it's something we hold here. Our outreach group at the UGS puts it on. It's always nice to have different volunteers come in and work with all the school groups and kids that come through to learn about Earth Science. And we have a whole bunch of little booths and activities to do with the kids. Gold panning. I don't think we have any gold in it. But there's Pyrite. And we have a stream table. Yeah, full is gold. So all kinds of, and then dinosaur and I think there's a rock talk. And I highly recommend it. I'll be doing it. Contact Jim Davis, jmdavis at Utah.gov. He will help figure out what your schedule can allow for. Also worth noting there's a John Wesley Powell event coming up at the National History Museum of Utah up there in the foothills on September the 22nd. And they are honoring the upcoming, I think it's 150th anniversary of the John Wesley Powell Colorado River exploration, the epic journey down the Colorado, mapping the geology and exploring the American West. U of U is putting on a lecture by Arlo Weil, I think his name is, on originic processes on September the 17th. So they put on a number of guest lectures and stuff. It's worth keeping your eyes on their lecture schedule because they have a number of good people speaking there. And then there's an upcoming AEG meeting this week on the 13th. Is anybody here with AEG? They have Dr. Rigby coming in to talk and he's going to be talking about munitions with some type or another. I'm sure it's related to geology though. So they're definitely worth. And then one more thing on September the 29th, Brian McInerney is going to be talking about climate science at the downtown library. He came here and did a talk, I think earlier this year, it was pretty good on climate. He works for the U.S. Weather Service. So his talks are usually pretty good. Great. As a reminder, I did put out a little bag for recycling your cans, if you can do that, please. We usually have a bigger container, but we don't this time. Any other announcements that I missed? Could you talk about your short course, Bonneville? We have that short course on the UGS main page. Oh great, there's flies on the table. That's great. Thanks, Adam. Okay, I'd like to... Oh, go ahead. We had a lot of golf with the common players, and there's a lot of injuries. And we're looking for... If you've got prizes to the golfers, if you recognize, anything you want to donate to the golfers? Oh great. I meant to mention that. Thank you for reminding me. Yeah, the golf tournament is coming up, and it's benefited this organization quite a bit in the past. We take turns hosting it between the various geologic organizations here. Who's hosting it this year? The mining engineers are hosting it this year. Next year we're supposed to host it. We had such a part coming on that event. Oh man. So maybe I should pick up golf, I don't... You don't really have to know how to golf. You drop the course. But the proceeds go to benefit our non-profit and students, of course, so it's definitely a worthwhile endeavor. We usually get pretty good sponsorship support. So if you're interested in being a sponsor or a golfer in the future, just keep in mind that's something we do every year. Usually we raise like $1,000. The whole economy's got $7,000. We need $2,000. Since we got parking out. Yeah, we may be flushed with cash this year because of the recent meeting, but it's definitely important. It's something that the board has discussed quite a bit is making sure we maintain a balance between our scholarship and what we're giving away and what we're bringing in. So that's an important source of income for the UGA. Okay, without further ado, I'd like to introduce Dr. Dennis Newell. He is the head of the isotope lab up at USU, my alma mater, and his wife, Alexa Alt actually, spoke earlier this year and that whole family presenting here. He got his PhD from the University of New Mexico. He researches CO2-rich crustal fluids. He did his postdoc at Los Alamos National Lab. And now he's a professor here at USU. Did I leave anything out, Dennis? No, it's good. Great, thank you. Oh, like this. This is for our online followers. This is like the task to get this thing on. All right, well, thanks for inviting me, I guess, down here and feeding me lunch. It's a pleasure to come talk to you. And I'm glad I'm not following my wife, Alexis, right away because she usually gives really good talks and mine will not be as good as hers, I'm sure. So what I'd like to do today is talk to you about Great Salt Lake Microbiolites, which a number of folks in here I'm sure have worked on, looked at, thought about. And this is a new research avenue for me. This was not exactly my specialization. I came here in 2013 from New Mexico, where I'd worked at Los Alamos National Lab for a while. And I was doing experimental geochemistry on things like CO2 sequestration, unconventional oil, stuff like that, nuclear waste. But I got involved in this project. I'll talk a little bit about how that happened. And it's been really interesting because I've met a number of folks, including Mike Bannenberg in the back. I've learned a lot about this system from him. And then a new faculty member at Weber State, if you haven't had her come give a talk, that might be really interesting. And she's an expert on Microbiolite. So I've sort of jumped into this. At first I was mentoring an undergraduate student, a really excellent undergraduate student, Jordan Jensen, who's now going to be starting with ExxonMobil this next year. He needed a senior thesis project, was interested in geochemistry and isotopes. And because the lake level had dropped so much, these were exposed and it opened up an opportunity to look at them. Okay, next slide. Cool. All right. So a little bit more about me. As it was mentioned, I'm the director of the Utah State University stable isotope lab, a lab that's pictured down here that's been growing over the last five years or so. And what am I? I'm a geologist first by training and a geochemist. And during my doctorate work, I really specialized in stable isotope geochemistry. But I am a geologist. And so all of the work that I do is pretty much founded in some sort of field work initially. And as you mentioned, I'm interested in crustal fluids. So here's my recent field season this last summer in Peru in the Altiplano, where this is a bubbling hot spring and I'm interested in the isotope geochemistry of those gases to give me the provenance of the volatiles like the carbon where it's coming from. And so that theme takes me into really looking at stuff at Great Salt Lake too, water rock biosphere interactions, really trying to understand using isotope geochemistry, what is going on in these geologic systems that we observe. And then just a plug for the lab. I know you've got excellent facilities here in Salt Lake City, but we're also a growing, and we have more of maybe a personal touch in terms of if you have work that you want to do in the lab, you can contact me and I'll work with you pretty closely on getting stuff done. We can do oxygen, carbon, and hydrogen and stable isotope ratios in water, oxygen, carbon, and all a variety of carbonates. We can do carbon, nitrogen, hydrogen, and oxygen in organic matter, and we have some work on tree rings that we're doing. I have a whole bunch of biologists that come in and want to do various bits of fish, you know, fish brains, fish scales, all kinds of things. And I'm also developing some techniques to look at hydrogen and hydrous minerals, such as muscovite or biotite that might be growing, say in a fault zone, or you have it in a xenolith that's transited from the mantle to the crust. So anyway, that's kind of what I do. I'm an assistant professor. Hopefully, next time you see me, I'll be an associate professor. Next slide. Okay, so back to what I'm talking about today. So, you know, due to the historically low water levels, you know, these microbial deposits were exposed all around Great Salt Lake. And this is a photo at Buffalo Point on Antelope Island. And again, how I got involved in this is I had an excellent undergrad student who was looking for a project. And there were a number of folks in our department of geology who are interested in a variety of things at Great Salt Lake. And I'm, you know, kind of new, poking around and they're like, well, you know, the lake is really low and we know these deposits are exposed. You know, maybe there's something interesting about those. You know, people look at these in the marine systems, et cetera, et cetera. So I started doing some research on what, you know, what exactly is a microbial item. And now the light is, but I really, you know, this was kind of new to me, brand new to me, to understand what we could learn from these. And it turns out that you can learn quite a lot from them. And it rolled right into the kind of things that I'm interested in. Basically using some sort of geological record that we can access today to say something about, you know, the processes and the water chemistry that were responsible for their formation. And this has led into all kinds of new questions and unknowns and whatnot. Thanks. Okay. So this is not good. These next couple of slides are going to be completely reviewed for most people in this room. There are a few students, so, you know, it's a good teaching opportunity for me. Put us in a little perspective of where we're at. Again, I'm going to be talking about microbialites in Great Salt Lake. And of course, Great Salt Lake, we, is really, you know, I guess we'll call it, I get beat up sometimes, you know, use the word like remnant of Lake Bonneville or a relic of Lake Bonneville. Great Salt Lake is really in the cycle of big and small lakes that have happened throughout the, you know, the Pleistocene. We have these pluvial or glacial periods that are wet and we have large lakes all throughout the Great Basin, filling in these, you know, these low lying flat areas. And then due to climatic shifts, you know, these shrink and we get these smaller, isolated hypersaline lakes throughout. And this is just the latest cycle that we're sampling here. Next slide. And then of course, the associated hydrograph. I will say, and I've learned a lot about this hydrograph and there's lots and lots of data that goes into this. A lot of it is, you know, sort of geologic and geomorphic, you know, observations in the field that are coupled with a whole variety of geochronological techniques, you know, a lot of radiocarbon dates. And this part of the hydrograph is fairly well pinned with a lot of radiocarbon date. Not that there isn't any uncertainty into it, but, you know, we can say from, you know, 30,000 years ago to about, you know, 17 and a half, you know, Lake Bonneville with some fluctuations was generally growing and becoming larger and larger. And then of course, there's the, you know, catastrophic Bonneville flood out of the north into the valley that I live in, which is an interesting story in itself, dropping things down to the provo level that all of the Utah universities are built onto. And then due to climatic changes going into the dry parts of the Holocene, you know, we moved into the Great Salt Lake stages. Now, this part of the hydrograph is drawn in here with curves, but I've been reminded that this is not well constrained. We don't know a lot about this part of the hydrograph, and that is in part what makes it interesting to look at these microbialites because they are basically being exposed at these lake levels. And so I'm not going to be refining this hydrograph directly, but my hope is to understand something about how the chemistry of the lake has changed in this part of the history. Okay, all right, so Great Salt Lake microbialite. So microbialite is this general term that's sort of an accepted term to be used for these carbonate deposits that are associated with some sort of microbial activity and microbial construction. So the microbes, the consortium of things like cyanobacteria and other primary producers are involved somehow in either nucleating carbonate or triggering the precipitation of that carbonate, and they grow in these environments. If they have a nice layered, laminated look to them, we call them stromatolites. If they don't, they have some other sort of texture, we call them frombolytes, but the over-encompassing term we use for these is microbialites. And Great Salt Lake has a lot of them. You know, all around the whole perimeter of the lake, in green here is where these are found. There's, you know, in the past, there's quotations like it's the largest, you know, modern extent of microbialites on Earth. But of course, that would suggest that these are all actively growing microbialites. That they're, I won't say alive, that they're, I guess I could say they're alive. They're alive. We look at them now, they've got some stuff on them, some biomass that's growing on them, some paraffitin of some sort. But is that actually the consortium of organisms responsible for their growth? And were these all just sort of modern-day things that we see, or they have a longer history? There's all kinds of sizes and morphologies. Mike has shown me many locations around the lake, and he is really the expert on where to find these things and understand what they look like. Here's one that's, you know, fairly well lithified that's exposed on the meter scale. There's some that are much smaller, much more poorly lithified. There's some that, you know, the longshore wave action gives you sort of these linear features. Mike has found some up to, I would say, like three meters in diameter. So they can be quite large. And you can, you know, see them in Google Earth imagery. They're associated with all kinds of interesting features around the lake. And so it is really an interesting spot to work. So why should we study these? Well, from my point of view, perhaps these are a proxy for lake biogeochemical and hydrological changes through time. I'm not nearly the first person to say this. People have been looking at these types of deposits for literally decades throughout the world. Just not at Great Salt Lake because they've been underwater. You know, so that is inhibitous being able to look at them. Modern and ancient lakes. So here's, you know, you've seen green river formation, microbial lights, kind of a classic example where folks have worked on understanding the geochemistry of that lake through time through looking at these deposits. Of course, microbial lights are an excellent reservoir for petroleum. Some of the world's largest, you know, modern, new finds have been in marine microbial lights. And so it calls into question, how do they grow? How do they preserve this porosity? Is it primary? Is it secondary? So there's reasons to study these for analogs for exploring for hydrocarbons. And then astrobiology. Stromatolites, you know, are some of the earliest sort of, you know, more complicated microbial communities on Earth. You know, you can push these back three plus billion years, maybe three and a half billion years. We see things that look like these in the fossil record. And so it's a way to sort of understand life on Earth. And also if you're going to say Mars and you have a rover driving around or some sort of drone and you're taking imagery and you can start imaging things that look like this, they may be biosignatures. They may or may not be biological, but it's a hint of where you might look. So this is, NASA is interested in NASA's bin out in Great Salt Lake recently to look at, you know, these types of things. Okay. So open research questions. Does microbial carbonate and the organic matter that's trapped inside of these as they grow, give us a record of lake composition and biogeochemical cycling? All right. So meaning, you know, are these things primary? Do they give us a primary record? Or have they been changed, you know, because if like anything geologically, considerably, then maybe the signal we're looking at is not primary. And this leads us to understanding how old are these? You know, are they modern? If they ancient, how ancient are they? When do they grow? Are they growing today? How do they grow? These are things that we don't necessarily understand, especially at Great Salt Lake. And so I'm just going to be touching on some of these things, not all of these things. Okay. So my approach, of course, rooted in going out and doing field work and understanding where these are, you know, and sampling these, is to use stable isotope geochemistry coupled with some geochronology to look at these and understand, are they preserving a record of the lake? And if they are, what can we say? You know, again, here's work from the 80s in Kenya on a, you know, a carbonate type lake with microbialites growing. And this is, you don't pay attention to the scale, but these are carbon and oxygen stable isotopes. And you note that they are varying together. They are co-varying through time. Right? So that suggests to an isotope geochemist that something is going on that is affecting both isotope systems together. And so that might be tracking something in that lake that we can understand. We might be able to use that as a proxy for the composition of the water or some process, including like transgressions and regressions. We'll change the water chemistry. What is the source of water coming into the lake and helping these beings grow? Is it lake water? Is it groundwater? Stuff I won't get into in detail today, but nutrient cycling, you know. The consortium of organisms that's living in the lake, are they fixing nitrogen or they somewhere else in the nitrogen cycle? We have, you know, evidence for big boosts in primary production, like we see in some places like Utah Lake, right? Where we get these algal blooms and then you have die-offs. Do we have evidence for stuff like that being preserved in these? And then geochronology on these can be a challenge, right? So we're dealing with carbonates in a carbonate lake. So right away, anybody who works with radiocarbon is thinking, well, there might be a problem there. We might have something called a reservoir effect where we have long residence time dead carbon in there that's affecting our ratios. Or perhaps we don't. Perhaps the residence time of carbon is short enough at certain times that those ages are okay. But how do you figure that out? Well, one way is to date multiple things, you know, to double or triple date to see if you get consistent ages. I'm working on this approach, right? Today I'll only show you some ages from organic matter and these things. Okay. All right, so study locations. So again, they're located all around the lake and Mike is working in many, many locations. I've been to a few of these and I have samples and data from where the stars are. Today I'll be primarily presenting data from some microbialites here at Buffalo Point and Antelope Island. I have a lakeside sample from Mike that I've done a little bit of work on and we also have one from the North Arm. All right, so these come in all shapes and sizes and I did mention a little bit the definition of microbialite and instrumentalite versus thrombolyte. So here I've sectioned a number of different ones and if it was a true stromatolite you would see this beautiful sort of concentric lamination that really looks like tree rings or it looks like a stalactite when you cut it in half and you see these nice bands. Most of these don't show much of that. You see some like here and this is one from the North Arm. You see some of this sort of banding here. This has a really coarse. If you kind of squint at it, there's kind of a coarse banding to it. This one here has this sort of punky porous core and then you have some denser stuff with a little bit of banding around it. So this kind of stuff here we call it a clotted texture or a thrombolyte for clots and so there's these sort of carbonate cement clots that are in there and then a lot of porosity and these things have, I mean it's carbonate that's growing so it's trapping and binding anything that's there. So there might be the primary carbonate that's actually gluing things together but then the lake is full of pellets from Brian Schribb. There's Brian Fly casings. There's lithic fragments. There's uids and all of those types of things are getting incorporated into this. So when you go in and decide that you're going to subsample or work on it you have all of those things there and you have to be smart about what you say here's a Dremel tool go sample this you need to train them on what they need to go in and subsample otherwise you can get a piece of Cambrian limestone which is not going to be what you want to measure back one that's okay I'm going to bring this up, this is foreshadowing there's also some things that show these finely laminated carbonates kind of swirling through here around this other stuff I'll bring that up later these here are the reason I show them and it's this laminated carbonate it's not kind of encompassing something like it was like an outer growth rim it's actually cross cutting it it's coming up through them so it looks like there's channels of fluid moving up through some of these and then there's tightly laminated carbonates associated with those so that's something we're kind of interested in is what is causing that morphology and is it a hint for how these are growing okay now you can go zoom in a little bit I mentioned that it's important to know what you're sampling and we want to understand whether or not the isotope signals that we get are primary or secondary and so we have to go in and do you know, SEM work you know, just observation work, thin section work to see if you've precipitated new stuff if you've dissolved stuff out is it made of something you shouldn't be sampling at all so here's sort of two millimeters, sort of thin section scale and then SEM image on a scanning electron microscope of some part of this microbiolite over here and we see we have all these sort of acicular arachnite grains that are all tightly grown in there you also see these weird, I don't know quite how to describe them, but they're you know, they're submicron scale little bulbous mats of carbonate, it's all carbonate and so that almost gives you the impression some people would say oh that looks biogenic I don't know but you know, you're getting these little microspheres, nanospheres of carbonate that are growing in here so I look at a texture like this, it's pretty you know, indicative of something that hasn't seen a whole lot of like dissolution and secondary precipitation of something else so if I can sample areas like this, I'm going to get you know, better data than other locations like the next slide so there's also a lot of this stuff here, which is poop right, so these are brine shrimp pellets and this is a pellet here, the pellet core and this is again an SC image and the edge of it it has these fine little laminations so there's kind of this carbonate crustacean of the pellets so they're getting trapped in these microbial lights and then they're getting coated in carbonate, right but if you were to go in and basically sample a whole lot of this stuff, yeah you're probably going to get this carbonate signal but we don't really know when it formed so what's going to matter is going to be telling you something about the brine shrimp poop not necessarily about the microbes that are living in there, so you got to be careful on these things, okay alright, so I am going to present some data and it's going to be stabilized hope data, so here's just kind of a quick primer on what this means, alright so all the numbers I show are going to use standard what we say delta notation, right so we would say this is the delta carbon-13C and so what that is is it's related to the way we measure the isotopes, the reason this exists it's much much easier and more precise to measure isotope ratios than absolute isotope abundances so we don't collect carbon-13 in a cup and carbon-12 in a cup and then get the ratio, we measure you know compounds with a certain signal and a certain ratio of carbon-13 and carbon-12 to a standard, so this is all basically measured relative to a standard that way we can compare it internationally from lab to lab around the world and so this all kind of came out of the early 50's when this technique came about and now we have these international standards that everybody uses and the standard is that we ratio the common, I mean the heavy rare to the common, so for carbon like 1% of carbon-13, 1% of carbon is 13 and 98.9 is 12, and so that we do that ratio to a standard we multiply it times a thousand so it's a nice round number and then it's in per mill notation. Note that carbon-14 isn't here, these are stable isotopes so we're not considering radiogenic carbon in this case. Other ones that we'll talk about here are delta deuterium and then delta-18-0 alright, so the plots I show for these will be delta-18-0 and delta-13-C in per mill these are relative to PDB and so what do these numbers mean? Before we even talk about anything here, what do these numbers mean? Again, they are relative to an international standard they're useful for comparison from place to place to place. So if we go out and we measure say average limestone, we measure organic matter, we measure CO2 coming from the mantle, we measure all these different things, we can get signatures they can be used as finger printing it's tracers, so we can understand where things are coming from or processes, we can mix one water with another water and we're going to get isotope mixing we could have degassing, we could have kinetic processes these biological processes that change systematically change those isotopes so that's why we use these, they're numbers that intrinsically don't mean anything because they're just ratios, what we want to do is compare them to other known ratios from other things and then see what kind of patterns we have and that's how we use them. So here are two microbial light samples Antelope Island and Lakeside delta-18-O versus delta-13-C the red and the blue dots are just giving you an idea of kind of where we sampled, it's not exactly where we sampled and then this is just a scatter plot so the first thing you see is that the antelope island and the lakeside form slightly different arrays with a positive correlation right, there are, you know, r-squared are okay, you know, there is a positive correlation there, alright, great so our job now is going to be, does that mean anything, is that primary for reference here are uids that are shoaling around presumably close to modern you know, whatever that means along the lakeshore and that's where they form but they could be older ones that are reworked and rolling around alright, next slide so people have worked on this in closed basin lakes and Great Salt Lake certainly is a closed basin lake so we should hope that it behaves like one and Talbot has a nice paper from 1990 where they've looked at carbonate from closed basin lakes all over the world looking at lake core carbonates like you drill down and you get nice laminated lake core or you grab microbialites, Great Salt Lake actually is in the legend here so there's some Great Salt Lake data in there and they see this positive correlation and that's because whatever is affecting oxygen isotopes is also affecting the carbon isotopes so if we think about it in a simplistic way we have a lake level at a certain level and we have, you know, the mix of hydrologic system, you know, delivering groundwater and surface water to that lake and precipitation and whatever those ratios are they're representative of what's coming out of the basin the carbon is representative of what's coming out of the basin and what's being consumed in the lake and then you go through a period of change let's say we fill that lake or we shrink that lake if we fill that lake that means things are getting wetter we're adding water to the system we're perturbing that balance in that closed basin lake and likely the water that's coming in is what we call meteoric it's rainwater and in general those isotope ratios will be lower than whatever is in the lake so then we would expect that ratio to go down so we would have a downward trend those ratios corollary to that is the lake is drying up and it's evaporating which is certainly what we see in Great Salt Lake when we evaporate the light isotopes like oxygen 16 will leave the water preferentially to the heavier isotopes heavier isotopes stay behind so the ratio gets higher and higher and higher in the lake so we have a drying period we'd expect the isotope ratios to get higher so you might look at a trend like this and suggest that that's what's happening in that system that we're looking at periods of time when the lake level was relatively higher or relatively lower that's a simplistic view of that because there's a lot of other things that go into it but we can kind of work with that and you can get in I won't get into it but you can get into mixing in lakes are you are you in a shallow lake that's overturning a lot and you stirring up the buried carbon and consuming it are you in a in a seasonal overturn Meramex is sort of situation where you have bursts of primary production at certain times of the year that affect your carbon isotope so you can learn a lot from what's going on in a lake looking at these okay so here's a smattering of data from Great Salt Lake from a variety of different deposits this array here the black squares is that Antelope Island microbylite that I already showed the red one here is the lakeside one and there's some other data on here some other carbonates microbylite so you see some with these positive correlations and some they have different slopes and do but then you also see some that have a negative correlation and that's very strange that's very rarely reported in the literature in fact you can dig and dig and dig and it's very difficult to find any explanation for that so I'm struggling with an explanation I have an explanation for it whether or not it's a good one or not I don't know but for for reference I've kind of put the modern lake water this down here is not the carbonate this is the modern lake today or at least over several years kind of wet season dry season you know sort of late August you know April you know different you get different in members you also get this negative correlation so I'm attributing this to you know we're bringing in fresh water fresh water brings in nutrients in the spring we get bursts and boosts in primary production in that point in time that's going to cycle carbon faster that's going to drive the carbon isotopes up meanwhile the oxygen isotopes are going down because you're bringing in fresh water that could explain a negative correlation the other thing that's important about this is we want to evaluate whether or not the deposits that we look at today are precipitating from today's lake water or not one test is to ask if they're in isotopic equilibrium there's all these equations that have been empirically determined that you know are the basically the oxygen isotope thermometer for carbonate so if you know the water and you know the carbonate you can figure out the temperature alright so what I can do is I can take the known water and the measured temperatures and say well this light blue parallelogram is the carbonate that would precipitate in equilibrium with that and you'd say okay well some of the carbonates look like they could be from the modern lake water the uids for example but then there's a lot of stuff that absolutely cannot come from the modern lake water these really really high values are far far out of equilibrium with the current lake water and the lake's pretty low this suggests that you've had some process in the past that had enriched these isotopes much more so much longer residence times it's hard to imagine that you really had more relative evaporation given that the lake is a historic low stands so this does suggest that we're looking at some snapshot of chemistry at a different time next another way of looking at whether or not we show co-variation across these you know these microbialites and is there any sorts of patterns we mentioned sort of stalactites and tree rings and you expect maybe those things are tracking something that's happening through time so if we look at through time if you use the center of the microbialite to the rim as time from 0 to 10 centimeters here this is what the isotopes look like so the carbon and oxygen are tracking one another they should be because we have a pretty strong co-variation except in a few spots here so it does look like there is some sort of you know isotopic stratification in the microbialite which is important because that suggests that it all hasn't been reset by diagenesis if we had a wholesale dissolution and reprispitation it would kind of you would just blend out all that it would you get homogenization of your ratios eventually and so we are preserving something through time and again from a very simplistic modeling standpoint very simplistic you can take those oxygen isotopes and just do a mass balance and say alright what do I need to do to the lake volume to get the isotopes to change this much and to go from minus 4 per mil to minus 1.5 per mil or minus 1 per mil the lake would have to drop by 28 percent in volume the volume of water would have to be 28 percent lower or it would have to be 16 percent higher or 12 percent lower depending on how you look at it here so this you could say this is a way of looking at when the lake got bigger when the lake got smaller but it's a simplistic viewpoint this is a work in progress there's other stuff that can go on you could have lake Bonneville sitting there at a high stand and not fluctuating much for a couple thousand years and you could also see some trends just because the residence time of certain things in the lake you know are there it's a little more complicated than this shows but this is some of the stuff you could do with it next slide and of course we'd like to know how old this is so initially I was quite concerned about the reservoir effect and didn't have a lot of money so we decided that we would extract organic matter from some of these layers so we go in, draw out a bunch of stuff dissolve the carbonate away and basically get just the organic matter and submit that for AMS these are the ages that we get in calendar kill years so those of you who have noticed already that doesn't seem to be a nice time stratigraphy, the core of this appears to be younger than this layer and then it gets younger again so that's one observation you make you're like hmm and then another one you might make is that this is really from right at the rim of it so right at the very edge of this and this is the organic matter from this that at least in its current form you know this hasn't grown much in seven and a half thousand years since the ultathermol this particular microbiolite has been occupied by you know some sort of shrub like stuff over and over again whenever it's wet but it doesn't appear that it's grown in terms of carbonate precipitation in a significant way at all that we can determine at least from this so that's an interesting observation as well I can try to argue if I can go away with these which is difficult but I will say that we're we've got the carbonate out for dating right now and we're also doing some uranium thorium dating on these so we'll have three independent ways of looking at the age of these we can help then arm wave a little bit better one argument is that the center of this is pretty porous and this is pretty tight stuff you go out there and you you know kind of pry one of these microbiolites you'll note that there's fluid upwelling inside of these and you break them open and some of them give you this nice sort of sulfury smell so you know that there's some microbial activity going on and so the primary organic matter that the microbialites would be encasing is from photosynthesis is primary production but that rotten egg smell is telling you that there's anaerobic stuff going on you've got some heterotrophic stuff going on so you have later microbial activity that's ongoing so it's quite possible these are mixed ages but you got old carbon and young carbon mixed together and you have no way of figuring out what's what we'll test that hypothesis okay so anyway they're old older than we thought this is a compilation of you know the dates I have here some published stuff the purple dots problem with the purple dots is I don't know what this these researchers did I know that they're carbonate ages but I don't know if they're a rim of a carbonate or if they took a whole microbialite and kind of crushed it up they could be mixed ages I'm not really sure but there's overlap a little bit with with ours and they do have some that are you know only a few thousand years old but note that at least in this sampling set we're not seeing anything really really young here's the lakeside one this is not my age dating these are these are older published ages they have ages from both the organic matter and the carbonate on these so it's a double date for that puts it around 15 ish of course doesn't match up well with this hydrograph it doesn't mean the hydrograph is wrong it just means that this this age might be a little problematic but there are some that at least go back maybe 15,000 years okay so that's what you know the great Salt Lake microbialite isotope geochemistry tells us but we shouldn't look at this in a vacuum because there's been quite a bit of other work done on Great Salt Lake and the Bonneville Basin both in terms of lake cores where lake cores are kind of the traditional way of looking at paleolimnology like we go out we put in a sediment core we pull that out we find an age model way to date the different layers figure out how how long it took to deposit those and then we can go in and do all kinds of different chemical things including carbon and oxygen isotopes on the carbonates so that's been done at some shallow borings in Great Salt Lake itself and then way out here there's the Blue Lake Marsh core that was on the really on the western edge of where Lake Bonneville is and then there's also some caves Cathedral and Craners caves they have some lake carbonates are precipitated in the cave and the lake level is that high and so those were dated and there's isotope data for that so that's all smattered on here and color-coded first takeaway you have is everything's giving you this most everything is giving you this positive co-variation positive correlation which it should because we have a closed basin lake even when Lake Bonneville existed it was still the it was a closed basin it wasn't draining out it wasn't water wasn't coming in and going out right it was coming in and staying in there and fluctuating there is some data sort of falls off that there is one of these negative trends in there in one of the lake carbonates which is interesting I mean down here I have this sort of hydrograph with some color bars on here that are coded to these different colors appearance what I'm going to do is I'm going to show one graph that is pre-flood and one graph that is post-flood just as a bit of an arbitrary way to look at two state you know two snapshots long snapshots of the lake so there's here's pre-flood alright so pre 17.2 thousand years or 17.4 thousand years ago and that's looking at these records here so we have Blue Lake Marsh core from the western side of Lake Bonneville we have these caves and we have this green line which is this compilation of sediment course from Great Salt Lake this is this record here the isotope data is good but I don't have good age data from that it's basically from about 30,000 years to modern but I have no idea what goes with what so I'm just putting the whole record on there this is sort of a Great Salt Lake record that probably is pre and post-flood but you see a nice positive correlation Lake Bonneville time some things to look at it's like alright my oxygen isotopes are minus 10 to minus 6 so that says something about the hydrologic system that's something about the water that's coming into the system these are the cave deposits they both show the same slope and the same oxygen isotopes slightly different carbon that's because one set of them is aragonite and one set of them is calcite and there's just a different fractionation factor for carbon for those they're essentially giving you the same story it has a slightly lower slope and you're a slightly more enriched than this Blue Lake Marsh core alright this step forward okay then when we go post-flood what we see is that record start to deviate alright so we have this nice sort of story and now we're starting to see you know out at Blue Lake Marsh we have you know for a while we have kind of the same trend then it steps out this way and then it just goes to noise so what happens there is like Bonneville is shrinking and eventually it becomes this no longer a lake and it's just sort of this wetland and now we're no longer getting any co-variability in those you're just getting noise there's different things affecting the carbon that are affecting the oxygen so you see the western part of it hydrologically being separated and then becoming not a lake and then Great Salt Lake forms and you get these isotopes that are stepped out over here much more to use a jargon term enriched or heavy as we get this evaporative lake in the in the Holocene so this this just snapshot of a few data sets shows that as maybe as we would expect as these big Pluvial Lakes shrink they become sort of segmented isolated sub basins and that those are then going to evolve somewhat chemically distinctly from one another and we know this from classic work done on Great Basin lakes that you can start with very subtly different water chemistries and then evolve to very like Mono Lake versus Great Salt Lake for example very different in members of chemistry but we all started with some big Pluvial Lake at some point in time so I think this is pretty interesting and just a little bit to leave kind of start closing this up is to kind of come back to this sort of problematic question that we have I've just interpreted a bunch of stuff that assumes that these things are recording something about Lake chemistry well we still don't know exactly how they form so this is from my you know intro geochemistry stuff right here is just an equation you can write for the precipitation and or dissolution of calcite right so if we're going to think about equilibrium chemistry we can perturb this and you know there's no biological thing in this yet but biology can affect some of those parameters we look at the current Lake water and just kind of do some modeling to it it's under saturated with respect to calcite so it's not going to precipitate carbonate readily it's just not carbon is cycling through that lake pretty fast which I think is important for considering the reservoir effect it may not be that large because the co2 that's dissolving in is rapidly cycling through that system so we're not building up a lot of bicarbonate in this lake photosynthesis when forming you know if you have a cyanobacteria consortium of microbes if they're photosynthesizing they can alter that local geochemistry to favor calcite precipitation if they're using the inorganic carbon or the co2 to make biomass they're going to basically take this out and if you remember and your little teeter totter if you move that you need to go that direction to balance that out and you may precipitate carbonate that would also affect the local pH that would be a little local story local risk just around where that activity is going on there's also the possibility that the microbes themselves are actively participating in the precipitation say that of the carbonate within their cellular structure this is stuff I don't understand but Bonnie's here and she can tell us about this and of course we don't know which microbes necessarily do this and we're not sure when this happens because the age of some of these suggests that this hasn't happened in a while another possibility is since the you know this is under saturated with respect to calcite we could also add calcium or add bicarbonate to that water chemistry you could just take a beaker of it and start adding calcium and solution eventually you can precipitate calcite so perhaps that's coming in from groundwater which is the next slide so again we're back to this laminated carbonate structures that we see in a lot of these microglytes that are vertical or subvertical and then here's that ladyfinger point there's a microglyte at the surface and there's a spring that's there the water is fresher than the lake it's really salty but it's about half as salty as the lake and it's isotopes are way different than the lake so that spring water there on a standard meteoric water plot of hydrogen isotopes against oxygen isotopes the blue line and the green line is what all of your rain and surface and shallow groundwater should look like you know worldwide and so we're plotting right on what our local meteoric water line what would look like so if you looked at bare river water drainage coming out of the wasatch it would probably be around here somewhere so that spring water that's coming up through this microglyte that's half as salty as the lake is primarily meteoric water our colleague Kerry Franz has put in a bunch of shallow just like meter deep shallow pysometer type wells you know out at the Ladyfinger Point area of Antelope Island and this is groundwater but it falls on a mixing trend between lake water this is lake water measurements I've made and so you could suggest that this groundwater is a mixture of lake water and other deeper ground where it is not shocking news but it suggests that near the shore of the lake you have two of these both of these systems existing and so perhaps this is something to the hypothesis that up blowing waters is contributing to the formation of these microglytes next slide and there are some features out there that are truly looking like their spring type carbonates Mike took me to this one out of near Buffalo Point which is this sort of big tower of carbonate that's got some stuff that looks like microglyte and it's got some stuff that just looks like a two foot tower and it's got some laminated carbonate here around the base of it and what they see it the big soda lake Nevada these one to three meter tall two foot towers that are forming due to basically fracture controlled spring water upwelling in the lake so this is a possible analog for how something like that would form so just to close it we think there's periodic microglyte growth through the Holocene the latest Pleistocene through the Holocene that may provide an additional proxy for great salt lake meaning a proxy for what the lake chemistry was doing and maybe something about the lake hydrogeology not so much for the hydrograph these aren't informing how exactly how high or low the lake was but it's saying something about the freshness or the saltiness of the water the CNOI stable isotope values that we see some of these are likely primary I have some new data for some that I didn't show today that look like they may not be so there's definitely possibility that you are going to mess up some of these so you got to look at everything careful eye intra-microbial isotopic variability may attract changes in basin hydrology and lake extent so in one microglyte just like a tree ring or a stalactite you might be preserving a record of what's gone on when that microglyte was under water now of course when the lake drops too much you're not getting that information so you'll have hiatus basically nothing happening and of course if the lake gets too deep that's going to shut off the microglyte microbial activity and then maybe switch to some sort of other carbonate precipitation activity looking more broadly we think of course that the isotope data supports the idea that Bonneville divided into isolated sub basins as things sort of got lower and drier and we're going to continue to work on this to try to understand the linkage between the geochemistry and the geochronology and try to answer some of these questions on how these form so that we can better understand the record and then I'll just acknowledge Animal Violence State Park for permitting our sampling of my undergraduate student funding from the university in different sources and then our my cross could be core facility for helping with imaging these thanks questions well Bonne could help answer that question I think the answer is probably yes that you get to a certain salinity and the microbial population that you have is going to be different than under low salinity conditions the precipitation of carbonate can be slightly modified by salinity you know the activity of water you know the activity of your solutions geochemically can be subtly changed but it's not a first order control there's other things you can look at in these I didn't do this here but you can you know it's calcium carbonate so it's calcium and carbonate but when it precipitates from salty water it takes in appreciable amounts of sodium and other ions into its structure so you can also go in and dissolve that and analyze essentially the trace elements that are in calcium carbonate and then you'd have a proxy for salinity you could look at sodium changes through time in a microbial light and that would be directly related to the salinity of the lake I haven't done that yet fine Bob or Lady Fingerpoint is the closest easiest walk so the Lady Fingerpoint parking lot you can just walk down and I think at the current lake level you'd be able to photograph them no problem I personally haven't done any quantitative work on that Mike has looked at you know the association of microbial lights along with sort of these macro polygons these desiccation cracks and some of those are associated with some of these lineaments I have not looked at it but that would be a logical thing to do in terms of where you would have groundwater upwelling sort of test that idea but I haven't done that work yet you certainly could I mean some of them yeah some of them that are poorly lithified you know they're these cow pie structures as they've been described because they're kind of hollow on the inside and once the lake level drops they kind of collapse on themselves but as they you know sort of dry out you know they they lithify and they get a little bit more you know encrusted they become more resistant at that point in time and so you could imagine that they're a little less you know subject to weathering at that point in time of course then they could get buried by sediment too so you know if your lake level comes up high you could inundate these things and that could sort of shut off activity in the chronology if you had a nice detail chronology that you should have unconformities definitely should have unconformities that would be defined by doing careful you know geochron work but that would take a lot of you know a lot of work and the first thing we need to do is understand which system gives us the best idea of what's going on we're pretty old the ones we've looked at so far the ones that other people have dated so far all seem to be old old being Holocene old not geologically old but there it is curious that you know all the components seem to be there today for microbial like growth what I've heard from a lot of some of the microbiologists is the organisms are there that could do this but there seems to be something going on in terms of either the preservation or the magnitude of carbonate precipitation that happens today in the lake that is different than in the past because we're not preserving or you know preserving the last few thousand to seven thousand years but as we date more of these and get more confident we might change that story and maybe there's locations where this is happening we just don't know that yet absolutely yeah so when you do any sort of calculations to understand you know what your isotopes mean you need to know something about that because yes it is you know both the solubility of carbonate and the fractionation factors are a strong function of temperature and of course carbonate has you know retrograde solubility so when it's colder it's more soluble that's why your hot water heater falls apart so yeah I mean and I don't yeah I mean the temperature in the past you know there's certainly going to be times when it would have been a lot warmer like the Holocene old to thermal yeah in wetter periods things would have been on average cooler but we do have cold conditions now at times in the lake right we have you know water gets down to you know 10C or 8C or something in the winter doesn't freeze but we have cold conditions now so we have kind of a full range what we need to understand is what water and when these things are precipitating right are they precipitating during the warm time you might hypothesize well we need the warmest conditions to favor this so in mid-summer something is when that's happening so we need to understand today what's going on then we can better arm wave about you know in the past because we do know that you know there's Lake Bonneville shoreline tooth is all over the place so at much higher much cooler conditions we were in the swash zone precipitating carbonates and some of them pretty thick oh yeah so that was from organic matter so if I was looking at the organic matter carbon stabilized so it would also be a mixed signal for the carbonate stable isotopes it's probably a little bit different unless you're actually precipitating you know more carbonate later and of course that would be a mix mixing as well it's a little easier to evaluate carbonates via thin sections and SCM you can look at the solution textures etc etc in terms of organic matter it's much more difficult you know you're basically extracting you know several milligrams of organic matter from quite a bit of carbonate and you have no idea it's originally I don't by looking at it in the bottom beaker so that's that's much more difficult so I think through again I think that's why we need to couple you know multiple geochron methods with the isotope geochemistry to understand you know how robust these values are because if they're all mixed that's a big problem we can't say a whole lot if you have any more questions we'll come up and talk to you in a second thanks again for coming in my pleasure